Method of operating flying capacitance converter

Abstract

The present invention provides a method of operating a flying capacitor converter (FCC) according to a quasi 2 level (Q2L) modulation, a method of operating a flying capacitor converter (FCC) according to a quasi 2 level (Q2L) modulation, a method of operating a flying capacitor converter (FCC) according to a quasi 2 level (Q2L) modulation, and a method of operating a flying capacitor converter (FCC) according to a quasi 2 level (Q2L) modulation. The FCC includes at least two flying capacitors, a first arm and a second arm. Each arm includes at least three series switches. One terminal of each flying capacitor is connected to the first arm, and the other terminal is connected to the second arm. The method includes simultaneously turning on each switch of a first set of switches on the first arm of the FCC to implement a first Q2L pulse. Each switch in a second set of switches on the first arm is then turned on simultaneously. After a pulse duration of the first Q2L pulse, each switch in the first set of switches is simultaneously turned off, and then each switch in the second set of switches is simultaneously turned off.

Description

Technical Field

[0001] The present invention relates generally to DC / AC converters, and in particular to a flying capacitor converter (FCC). The present invention provides a method of operating the FCC according to quasi-2-level (Q2L) modulation. The present invention also provides a controller for controlling the operation of the FCC and an FCC device including the FCC and the controller. Background Art

[0002] In power electronics, a circuit used to convert a DC voltage to an AC voltage is called a DC / AC converter. A DC / AC converter can be used as a building block to create a DC / DC converter. DC / DC converters are classified by their isolation type (e.g., isolated converter or non-isolated converter), voltage level (e.g., boost converter or buck converter), and switching mode (e.g., hard switching or lossless soft switching). The present invention relates to a DC / AC building block with FCC used in an isolated DC / DC converter.

[0003] An important concept in voltage source converters is dead time. Dead time refers to the blank time when both the high-side switch and the low-side switch of the converter are turned off. Due to physical limitations, it takes a certain amount of time for the switch to turn on or off. This leads to the possibility that when the high-side switch is off and the current is still flowing through it, the low-side switch has already started to turn on and the current is also flowing through the low-side switch. This situation may cause the input voltage to short out. The purpose of setting dead time is to avoid this situation and avoid any possibility of the switches being turned on at the same time.

[0004] An FCC is a converter that includes multiple switches (usually semiconductor transistors acting as switches) and multiple flying capacitors. The FCC can be operated according to multi-level modulation, which provides multiple (more than two) voltage levels as output, but the size of the converter increases due to the larger size of the flying capacitors. Alternatively, the same structure can be operated according to Q2L modulation, which provides only two voltage levels as output, but the size and cost of the flying capacitors are much smaller. Q2L modulation uses the dead time between the two series switches to actively balance the series switches via the flying capacitor voltage. Depending on the number of devices in series, the dead time increases as the number of devices increases.

[0005] Therefore, among other disadvantages, the large number of devices increases the effective dead time. Summary of the invention

[0006] In view of the above, it is an object of the present invention to provide an improved method of operating an FCC according to Q2L modulation. One object of this is to reduce the effective dead time when operating the switches of the FCC.

[0007] These and other objects are achieved by the technical solutions of the present invention as described in the independent claims. Advantageous implementations are further described in the dependent claims.

[0008] A first aspect of the present invention provides a method for operating an FCC according to quasi-Q2L modulation. The FCC comprises at least two flying capacitors, a first arm and a second arm, wherein each arm comprises at least three series switches, one of two terminals of each flying capacitor is connected to the first arm, the other terminal is connected to the second arm, and the two terminals of each flying capacitor are connected between corresponding pairs of switches on the two arms; the method comprises: in order to achieve a first Q2L pulse, simultaneously turning on each switch of a first group of switches of the three or more switches on the first arm; then simultaneously turning on each switch of a second group of switches of the three or more switches on the first arm; after a pulse duration of the first Q2L pulse, simultaneously turning off each switch of the first group of switches, wherein the pulse duration of the first Q2L pulse starts when each switch of the first group of switches is turned on; and then simultaneously turning off each switch of the second group of switches.

[0009] By grouping the switches (e.g. semiconductor transistors) into first and second groups respectively and implementing the Q2L pulses, the dead time can be reduced. Thus, the method according to the first aspect provides an improved way of operating an FCC according to Q2L modulation. Other advantages of the method according to the first aspect will become apparent from the further description.

[0010] In an implementation of the first aspect, in the first Q2L pulse, turning on each switch in the first group of switches slightly charges a first flying capacitor of the at least two flying capacitors and slightly discharges a second flying capacitor of the at least two flying capacitors.

[0011] In an implementation of the first aspect, in the first Q2L pulse, turning off each switch in the first group of switches slightly discharges the first flying capacitor and slightly charges the second flying capacitor.

[0012] Therefore, the method according to the first aspect can keep the voltage on the flying capacitor balanced or close to balanced even if the size of the flying capacitor is reduced. Therefore, the method according to the first aspect can also achieve a smaller flying capacitor.

[0013] In an implementation of the first aspect, the method further includes: in order to realize a second Q2L pulse, simultaneously turning on each switch in a third group of the three or more switches on the second arm; then simultaneously turning on each switch in a fourth group of the three or more switches on the second arm; after a pulse duration of the second Q2L pulse, simultaneously turning off each switch in the third group of switches, wherein the pulse duration of the second Q2L pulse starts when each switch in the third group of switches is turned on; and then simultaneously turning off each switch in the fourth group of switches.

[0014] In an implementation of the first aspect, the method further includes: in order to realize a third Q2L pulse, simultaneously turning on each switch in the second group of switches; then simultaneously turning on each switch in the first group of switches; after a pulse duration of the third Q2L pulse, simultaneously turning off each switch in the second group of switches, wherein the pulse duration of the third Q2L pulse starts when each switch in the second group of switches is turned on; and then simultaneously turning off each switch in the first group of switches.

[0015] In an implementation of the first aspect, in the third Q2L pulse, turning on each switch in the second group of switches causes the first flying capacitor of the at least two flying capacitors to slightly discharge and causes the second flying capacitor of the at least two flying capacitors to slightly charge; and turning off each switch in the second group of switches causes the first flying capacitor to slightly charge and causes the second flying capacitor to slightly discharge.

[0016] In an implementation of the first aspect, each of the three or more switches on the first arm is included in the first group of switches or in the second group of switches; and / or each of the three or more switches on the second arm is included in the third group of switches or in the fourth group of switches.

[0017] In other words, the switches on each arm of the FCC can be grouped into exactly two sets of switches.

[0018] In an implementation of the first aspect, the first group of switches includes all even-numbered switches from the first switch to the last switch along the first arm among the three or more switches on the first arm; the second group of switches includes all odd-numbered switches from the first switch to the last switch along the first arm among the three or more switches on the first arm.

[0019] In an implementation of the first aspect, the third group of switches includes all even-numbered switches counted from the first switch to the last switch along the second arm among the three or more switches on the second arm; the fourth group of switches includes all odd-numbered switches counted from the first switch to the last switch along the second arm among the three or more switches on the second arm.

[0020] In an implementation of the first aspect, the method further includes: regrouping the three or more switches on the first arm from the first group of switches and the second group of switches into a fifth group of switches and a sixth group of switches; in order to implement a fourth Q2L pulse, simultaneously turning on each switch in the fifth group of switches; then simultaneously turning on each switch in the sixth group of switches; after a pulse duration of the fourth Q2L pulse, simultaneously turning off each switch in the fifth group of switches, wherein the pulse duration of the fourth Q2L pulse starts when each switch in the fifth group of switches is turned on; and then simultaneously turning off each switch in the sixth group of switches.

[0021] In this way, during the next hold time, only the flying capacitor that needs additional charging or discharging will be operated. Therefore, a balance or near balance of the flying capacitor can be achieved.

[0022] In an implementation manner of the first aspect, the regrouping is performed if a charging rate of at least one of the first flying capacitor and the second flying capacitor is different from a discharging rate of the at least one flying capacitor.

[0023] In an implementation manner of the first aspect, the regrouping is performed when a voltage of at least one of the first flying capacitor and the second flying capacitor reaches a corresponding threshold voltage.

[0024] A second aspect of the present invention provides a controller for controlling an FCC according to Q2L modulation. The FCC comprises at least two flying capacitors, a first arm and a second arm, wherein each arm comprises at least three series switches, one of the two terminals of each flying capacitor is connected to the first arm, the other terminal is connected to the second arm, and the two terminals of each flying capacitor are connected between corresponding pairs of switches on the two arms; the controller is used to: in order to achieve a first Q2L pulse, simultaneously control each switch in a first group of the three or more switches on the first arm to turn on; then simultaneously control each switch in a second group of the three or more switches on the first arm to turn on; after the pulse duration of the first Q2L pulse, simultaneously control each switch in the first group of switches to turn off, wherein the pulse duration of the first Q2L pulse starts when each switch in the first group of switches is controlled to turn on; then simultaneously control each switch in the second group of switches to turn off.

[0025] The controller is used to execute the method according to the first aspect. The controller can be used to execute each implementation of the method according to the first aspect. That is, the implementation of the controller according to the second aspect can correspond to the implementation of the method according to the first aspect. The controller achieves the same advantages as the method according to the first aspect.

[0026] A third aspect of the present invention provides an FCC device, wherein the FCC device comprises the FCC according to the second aspect and the controller.

[0027] A fourth aspect of the present invention provides a computer program comprising instructions. When the program is executed by a processing device such as the controller according to the second aspect, the instructions cause the processing device to control the FCC to operate according to the method of the first aspect and its implementation, respectively.

[0028] A fifth aspect of the present invention provides a non-transitory storage medium storing executable program code. When the executable program code is executed by a processor, the method according to the first aspect or any implementation thereof is executed.

[0029] It should be noted that all devices, elements, units and devices described in this application can be implemented in software or hardware elements or any type of combination thereof. All steps performed by various entities described in this application and the functions described to be performed by various entities are intended to indicate that each entity is suitable for or used to perform respective steps and functions. Although in the description of the following specific embodiments, the specific functions or steps performed by external entities are not reflected in the description of the specific detailed elements of the entity performing the specific steps or functions, it should be clear to the technician that these methods and functions can be implemented by corresponding software or hardware elements or any combination thereof. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] The following description of specific embodiments in conjunction with the accompanying drawings will illustrate the above aspects and implementations.

[0031] Figure 1 An example of a 4-level FCC that may be used in the present invention is shown.

[0032] Figure 2 Shows Figure 1 Examples of 2-level, 3-level, and 4-level output voltages for FCC in FIG.

[0033] Figure 3 An example of Q2L modulation is shown, wherein according to the Q2L modulation operation Figure 1 FCC in.

[0034] Figure 4 Limitations of an exemplary Q2L modulation are shown.

[0035] Figure 5 shows the Q2L modulation operation according to Figure 1 The dead time during switching of the FCC.

[0036] Figure 6 An exemplary FCC that may be used in the present invention is shown.

[0037] Figure 7 The present invention provides a method for operating Figure 6 The FCC method.

[0038] Figure 8 It is shown that the FCC for cross-balancing flying capacitors is switched by executing the method provided by the present invention.

[0039] Fig. 9 A waveform of a Q2L modulation according to which the FCC is operated using the method of the present invention is shown.

[0040] Fig.10Shown are (a) an ideal scenario of balanced flying capacitors, (b) a more realistic scenario of nearly balanced (slightly unbalanced) flying capacitors, and (c) a scenario of further improving flying capacitor balance by exemplary regrouping of FCC switches.

[0041] Fig.11 The principle of regrouping the switches of the FCC according to the method of the present invention is shown.

[0042] Fig.12 The waveform of the Q2L modulation according to which the FCC is operated using the method of the present invention is shown after regrouping the switches. DETAILED DESCRIPTION

[0043] Figure 1 An example of a 4-level FCC leg of an FCC 100 that may be used in the present invention is shown. The FCC leg includes an upper arm (with transistors / switches T U1 To T U3 ), lower arm (with transistor / switch T L1 To T L3 ) and two flying capacitors C 1 and C 2 .

[0044] One way to operate the FCC 100 is full-scale 4-level modulation, which provides an output waveform consisting of 4 voltage levels, such as Figure 2 as shown. Alternatively, 3-level modulation or 2-level modulation (as described below) can be used. The number of levels can be increased by changing the design of the FCC 100 and is limited only by size considerations, as the capacitors required for this configuration are quite large. There are two main reasons for using a multilevel FCC. First, the maximum voltage of a single switch is limited, and in order to achieve higher voltage levels, multiple switches need to be combined. Using a multilevel topology, the input voltage can be distributed between the arm switches. Second, in the case of DC / AC conversion, the output noise of the multilevel topology is less, so much less filtering is required.

[0045] Figure 1 An example application of the FCC 100 in the example may be for energy generated by solar photovoltaic (PV) power plants, which needs to be converted to higher voltages for efficient transmission. Typically, these higher voltage levels can be 10kV, 20kV or 35kV. Currently there are no semiconductor transistors / switches that can withstand such high voltages. However, different multi-level configurations based on low voltage switches can be used to obtain the required voltage range.

[0046] operate Figure 1Another approach to the FCC 100 shown is to turn on or off the switches on one arm almost simultaneously. The turn-on signal can be applied to one switch, for example, T U1 , and then after a short pause, also called hold time (not to be confused with dead time), the next switch is turned on, e.g., T U2 The short pause ensures that the switch is fully switched and does not overlap with other switches on the same arm. However, in this case, the output voltage of the FCC 100 resembles a 2-level output with stair-step turn-on and turn-off edges. This operation of the FCC 100 is called conventional Q2L modulation, as shown in Figure 3 shown.

[0047] The main advantage of any Q2L modulation is that the flying capacitor C 1 and C 2 They are used as reference voltage only during the hold time. Therefore, the volume of these capacitors can be several orders of magnitude smaller than that required for multi-level operation of FCC 100. Another advantage is that FCC 100 can be used in a soft-switching DC / DC configuration, where the voltage capability of the DC / DC converter can be significantly increased by connecting several switches in series.

[0048] However, minimizing the size of the capacitors in the FCC 100 also brings a disadvantage. That is, the capacitor voltage needs to be continuously maintained by turning on the switches on each arm in a specific order, because any uncontrolled operation will completely discharge the flying capacitors, or completely charge the flying capacitors, resulting in excessive voltages on all switches, which may damage the FCC 100.

[0049] To achieve conventional Q2L modulation, different sequences of operations may be used during the arm conduction process. The goal of each arm is to switch from a fully off state to a fully on state and vice versa. The switches need to be turned on one by one. These switches can be either forward conducting, for example, T U1 →T U2 →T U3 , and can also be reversed. When the switch is forward-conducted, the voltage on each flying capacitor increases slightly. Alternatively, a reverse-conducting sequence can also be used to slightly discharge the flying capacitor. Therefore, in order to maintain the flying capacitor voltage near the required level, it is necessary to measure the voltage and decide whether the next sequence is forward or reverse before turning on.

[0050] Conventional Q2L modulation can be achieved with a large number of switches on each arm. However, the number of switches cannot be infinite. Since all transistors / switches have a finite on and off time, the hold time cannot be less than that time. Furthermore, depending on the switch, the hold time may be around 100ns to 300ns. Under this limitation, considering the shortest hold time of a switch to be 300ns, the output signal will not be a square wave (when using conventional Q2L modulation) but a triangular wave (such as Figure 4 shown).

[0051] In addition, a large number of switches increases the dead time, which is the blank time between switching the switch on the upper arm and the switch on the lower arm of the FCC 100. The dead time should be longer than the sum of the effective hold times of all switches on one arm. The dead time starts after the first switch on an arm changes its state (on or off) until the first switch on the opposite arm switches accordingly, similar to Figure 5 The situation shown.

[0052] The dead time is calculated to ensure that all switches are fully turned off. Figure 1 In the case of FCC 100 in , this becomes a problem when operating according to conventional Q2L modulation, because the total hold time of multiple switches increases. On the one hand, the dead time needs to be longer than the sum of the total hold times of multiple switches. Long dead times may cause parasitic resonances between the inductive elements of the turned-off switches and the internal capacitances. Therefore, the dead time should be as short as possible, but at the same time longer than all hold times.

[0053] In view of this, the present invention provides a method 700 and a method for controlling an FCC (eg, Figure 6 The controller is used to execute the method 700, which includes Figure 7 Steps shown.

[0054] Figure 6 The FCC 600 in the present invention includes at least two flying capacitors 601a and 601b, a first arm and a second arm. Each arm includes at least three series switches 602a, 602b, 602c, and 602d. One of the two terminals of each flying capacitor 601a and 601b is connected to the first arm, and the other terminal is connected to the second arm. Therefore, the two terminals of each flying capacitor 601a and 601b are connected between the corresponding pairs of switches 602a and 602b on the two arms. It is worth noting that the FCC used in the present invention can also be Figure 1 That is, the method 700 and the controller may also be used to operate the FCC 100.

[0055] The method 700 and controller may operate the FCC 600 to implement one or more Q2L pulses of Q2L modulation. For example, to implement a first Q2L pulse, the method 700 includes: Figure 7 That is, the method comprises a first step 701: simultaneously turning on each switch 602a of a first group of three or more switches 602a, 602b on a first arm. Figure 6 In FIG. 7 , only one switch 602a is shown in the first group. Generally, the switches in the first group are labeled 602a. Then, the method includes a second step 702 of simultaneously turning on each switch 602b in the second group of three or more switches 602a, 602b on the first arm. Figure 6 In FIG. 6 , two switches 602 b are shown in the second group. Generally speaking, the switches in the second group are labeled 602 b.

[0056] In addition, after the pulse duration of the first Q2L pulse, the method includes a third step 703: simultaneously turning off each switch 602a in the first group of switches, wherein the pulse duration of the first Q2L pulse starts when each switch 602a in the first group of switches is turned on. Then, the method includes a fourth step 704: simultaneously turning off each switch 602b in the second group of switches. Therefore, unlike the conventional Q2L modulation, in the method 700 of the present invention, the switches are grouped, and accordingly an improved Q2L modulation is achieved.

[0057] The method 700 and the controller may also implement the second Q2L pulse by using the switches 602c, 602d on the second arm in a similar manner. In this case, the method 700 may include the following steps: simultaneously turning on each switch 602c in a third group of three or more switches 602c, 602d on the second arm. Figure 6 In FIG. 1 , only one switch 602c is shown in the third group. Generally, the switches in the third group are labeled 602c. Then, the method includes the following steps: simultaneously turning on each switch 602d in the fourth group of three or more switches 602c, 602d on the second arm. Figure 6 , two switches 602d are shown in the fourth group. Generally speaking, the switches in the fourth group are labeled 602d.

[0058] Then, the method includes the following steps: simultaneously turning off each switch 602c in the third group of switches after the pulse duration of the second Q2L pulse, wherein the pulse duration of the second Q2L pulse starts when each switch 602c in the third group of switches is turned on. Then, the method includes the following steps: simultaneously turning off each switch 602d in the fourth group of switches.

[0059] The controller may include a processor or a processing circuit (not shown), which is used to perform, carry out or start various operations of the controller described herein. The processing circuit may include hardware and / or the processing circuit may be controlled by software. The hardware may include analog circuits or digital circuits, or both analog circuits and digital circuits. The digital circuit may include components such as an application-specific integrated circuit (ASIC), a field-programmable gate array (FPGA), a digital signal processor (DSP) or a multi-purpose processor. The controller may also include a storage circuit, which stores one or more instructions that can be executed by the processor or the processing circuit (specifically, under the control of the software). For example, the storage circuit may include a non-transient storage medium that stores executable software code, and when the executable software code is executed by the processor or the processing circuit, various operations of the controller are executed. In one embodiment, the processing circuit includes one or more processors and a non-transient memory connected to the one or more processors. The non-transitory memory may carry executable program codes, which, when executed by the one or more processors, cause the controller to execute, perform or initiate the operations or methods described herein.

[0060] As mentioned above, according to the conventional Q2L modulation (see Figure 3 )operate Figure 1 The FCC 100 shown is disadvantageous because the number of switches of the FCC 100 is relatively large and the switches are arranged in series on each arm. Therefore, the present invention provides the above-mentioned operating method 700.

[0061] Specifically, the idea of ​​the present invention is to group the switches 602a, 602b and switch the switches simultaneously in each group, but with a delay between the groups. Figure 8 As shown, in Figure 1 and Figure 6 In other exemplary FCCs 800 similar to the FCC shown, for example, the entire arm of the FCC 800 can be divided into exactly two groups. The switches 602b in the second group are S U1 , S U3 and S U5 etc., while the switch 602a in the first group is S in this case. U2 , S U4 and S U6It is worth noting that in this example, the first group includes all even-numbered switches 602a on the first arm, and the second group includes all odd-numbered switches 602b on the first arm (counting from the first switch to the last switch along the first arm). Similarly, the third group may include all even-numbered switches 602c on the second arm, and the fourth group may include all odd-numbered switches 602d on the second arm. The method 700 may implement single-step operation.

[0062] Fig. 9 The operation waveforms of the method 700 are shown, specifically showing the switching signals of the three switches 602a, 602b on the upper arm and the characteristics of the flying capacitors 601a and 601b. In addition, Fig. 9 (a) in corresponds to Figure 8 The upper part (branch) of the circuit, in which S is first turned on U2 , so that the flying capacitor C 1 (The first flying capacitor 601a) is slightly charged and makes the capacitor C 2 (The second flying capacitor 601b) is slightly discharged. Fig. 9 (b) in corresponds to Figure 8 The lower part (branch) of the circuit, in which S is first turned on U1 and S U3 , so that C 1 Slightly discharge and make C 2 Lightly charged.

[0063] exist Fig. 9 In (a), each switch 602a (S U2 ), and then simultaneously turn on each switch 602b (S U1 , S U3 After the pulse duration, each switch 602a in the first group is turned off simultaneously (S U2 ), and then simultaneously turn off each switch 602b (S U1 , S U3 ).

[0064] exist Fig. 9 In (b), each switch 602b (S U1 , S U3 ), and then simultaneously turn on each switch 602a (S U2 ). After the pulse duration, each switch 602b in the second group is turned off simultaneously, and then each switch 602a in the first group is turned off simultaneously.

[0065] The method 700 of the present invention can achieve the following: Figure 8 The two sequences (upper branch or lower branch) shown switch to maintain the voltage on the flying capacitors 601a and 601b (balanced or close to balanced). Fig. 9 As shown in (a), for the first sequence, each switch 602a in the first group is turned on to make the first flying capacitor 601a (C 1 ) is slightly charged and causes the second flying capacitor 601b (C 2 ) is slightly discharged. Then, each switch 602a in the first group is disconnected to make the first flying capacitor 601a (C 1 ) slightly discharges and slightly charges the second flying capacitor 601b (C 2 ). Similarly, Fig. 9 As shown in (b), for the second sequence, each switch 602a in the second group is turned on to make the second flying capacitor 601b (C 2 ) is slightly charged and causes the first flying capacitor 601a (C 1 ) is slightly discharged. Then, each switch 602a in the second group is disconnected to make the second flying capacitor 601b (C 2 ) slightly discharges and causes the first flying capacitor 601a (C 1 )Slightly charge.

[0066] In an ideal scenario, before the next turn-on / off, i.e., before the next Q2L pulse is implemented, changing the order (i.e., from the first order to the second order or vice versa) can keep all flying capacitors 601a, 601b balanced or at least close to balanced. Fig.10 In (a), the capacitor voltages are balanced. In practice, all flying capacitors 601a, 601b may have different tolerances, different capacitance values, and / or different internal parameters. Therefore, the charging rate of one capacitor 601a may be different from the charging rate of the other capacitors 602a, which may result in a slight imbalance, such as Fig.10 As shown in (b) in . Specifically, there may be slight differences in the parameters of the flying capacitors 601a and 601b, resulting in a slight imbalance in the voltage. On the other hand, the charging rate and / or discharge rate of the flying capacitors 601a and 601b are usually very slow because these capacitors only operate within the holding time (as described above), for example, in the range of 100ns to 300ns. In addition, the FCC operated according to Q2L modulation operates in a soft switching mode. Therefore, the current flowing through the flying capacitors 601a and 601b is very small. Therefore, in actual scenarios, the difference in flying capacitors does not immediately affect the voltage balance, but takes a long time.

[0067] In real-world scenarios, for example, when the charging rate of the flying capacitors 601a, 601b is different from their discharging rate, regrouping can also be used to improve voltage balance. The idea of ​​regrouping is that the switches 602a, 602b can be regrouped so that only the flying capacitors 601a, 601b that need additional charging or discharging are operated during the next hold time (Q2L pulse). This is shown in FIG. Fig.10 For example, when the second flying capacitor C 2 When the voltage on S drops below a lower limit or threshold, regrouping begins. U3 and S U2 Can be switched together as a new group, S U1 can be switched after the hold time, so that only the capacitor C 2 Charging. 1 The voltage during this time is not controlled, but because the discharge rate is very slow, the regrouping will occur at C 1 Once C 2 When the voltage reaches an upper limit or threshold, regrouping may begin again. Fig.11 and Figure 8 Similarly, the regrouping principle and switching sequence of the FCC 800 according to the method 700 of the present invention are shown.

[0068] For example, three or more switches 602a, 602b on the first arm of the FCC may be regrouped from the first group and the second group (as described above) into a new fifth group and a new sixth group, respectively. Such regrouping may be performed if the charging rate of at least one of the first flying capacitor 601a and the second flying capacitor 601b is different from the discharging rate of at least one of the flying capacitors. The regrouping may be performed when the voltage of at least one of the first flying capacitor 601a and the second flying capacitor 601b reaches a corresponding limit or threshold voltage.

[0069] Fig.12 (a) in FIG. 1 shows the waveform for implementing the next Q2L pulse after the switches are regrouped (similar to Fig. 9 First, each switch 140a in the new fifth group (now S U2 and S U3 Then, each switch 140b in the new sixth set of switches (now S U1 ). After the pulse duration, each switch 140a in the fifth group is opened, and then each switch 140b in the sixth group is opened simultaneously.

[0070] Fig.12 (b) shows the regrouping for achieving other Q2L pulses ( Fig.11 First, each switch 140b in the sixth group (now S U1 Then, each switch 140a in the fifth group (now S U2 and S U3 ). After the pulse duration, each switch 140b in the sixth group is turned off, and then each switch 140a in the fifth group of switches is simultaneously opened or turned off. It is worth noting that the "turning off" and "opening" of switches 602a, 602b, 602c, 602d, 140a and 140b are equivalent.

[0071] The present invention has been described in conjunction with various embodiments as examples and implementations. However, from a study of the drawings, the present invention and the independent claims, other variations will be understood and implemented by those skilled in the art in implementing the claimed subject matter. In the claims and in the specification, the word "comprising" does not exclude other elements or steps, and the quantifier "a" does not exclude a plurality. A single element or other unit may fulfil the functions of several entities or items described in the claims. The listing of certain measures in mutually different dependent claims does not imply that a combination of these measures cannot be used in an advantageous implementation.

Claims

1. A method (700) for operating a flying capacitor converter (FCC) (100, 600, 800) according to quasi-2-level (Q2L) modulation, It is characterized in that The FCC (100, 600, 800) comprises at least two flying capacitors (601a, 601b), a first arm and a second arm, wherein each arm comprises at least three series switches (602a, 602b, 602c, 602d), one of the two terminals of each flying capacitor (601a, 601b) is connected to the first arm, the other terminal is connected to the second arm, and the two terminals of each flying capacitor (601a, 601b) are connected between corresponding pairs of switches (602a, 602b, 602c, 602d) on the two arms; The method (700) comprises: in order to achieve a first Q2L pulse, Simultaneously turning on (701) each switch (602a) of a first set of the three or more switches (602a, 602b) on the first arm; Then simultaneously turning on (702) each switch (602b) of a second set of the three or more switches (602a, 602b) on the first arm; simultaneously opening (703) each switch (602a) of the first set of switches after a pulse duration of the first Q2L pulse, wherein the pulse duration of the first Q2L pulse begins when each switch (602a) of the first set of switches is turned on; Each switch (602b) in the second set of switches is then opened (704) simultaneously.

2. The method (700) according to claim 1, It is characterized in that In the first Q2L pulse, The turning on (701) each switch (602a) in the first group of switches slightly charges a first flying capacitor (601a) of the at least two flying capacitors (601a, 601b) and slightly discharges a second flying capacitor (601b) of the at least two flying capacitors (601a, 601b).

3. The method (700) according to claim 1 or 2, It is characterized in that In the first Q2L pulse, The opening (703) of each switch (602a) in the first set of switches slightly discharges the first flying capacitor (601a) and slightly charges the second flying capacitor (601b).

4. The method (700) according to any one of claims 1 to 3, It is characterized in that Also includes: To achieve the second Q2L pulse, Simultaneously turning on each switch (602c) of a third group of the three or more switches (602c, 602d) on the second arm; Then, each switch (602d) in a fourth group of the three or more switches (602c, 602d) on the second arm is turned on simultaneously; simultaneously turning off each switch (602c) of the third set of switches after a pulse duration of the second Q2L pulse, wherein the pulse duration of the second Q2L pulse begins when each switch (602c) of the third set of switches is turned on; Each switch in the fourth set of switches is then opened simultaneously (602d).

5. The method (700) according to any one of claims 1 to 4, It is characterized in that Also includes: To achieve the third Q2L pulse, Simultaneously turning on each switch in the second set of switches (602b); Then, each switch in the first set of switches is turned on simultaneously (602a); simultaneously turning off each switch (602b) of the second set of switches after a pulse duration of the third Q2L pulse, wherein the pulse duration of the third Q2L pulse begins when each switch (602b) of the second set of switches is turned on; Each switch in the first set of switches is then opened simultaneously (602a).

6. The method (700) according to claim 5, It is characterized in that In the third Q2L pulse, The step of turning on each switch (602b) in the second group of switches slightly discharges the first flying capacitor (601a) of the at least two flying capacitors (601a, 601b) and slightly charges the second flying capacitor (601b) of the at least two flying capacitors (601a, 601b); The opening of each switch (602b) in the second set of switches slightly charges the first flying capacitor (601a) and slightly discharges the second flying capacitor (601b).

7. The method (700) according to any one of claims 1 to 6, It is characterized in that Each switch (602a, 602b) of the three or more switches on the first arm is included in the first set of switches or in the second set of switches; and / or Each switch (602c, 602d) of the three or more switches on the second arm is included in the third group of switches or in the fourth group of switches.

8. The method (700) according to claim 7, It is characterized in that The first set of switches includes all even-numbered switches (602a) of the three or more switches (602a, 602b) on the first arm, counted from the first switch to the last switch along the first arm; The second group of switches includes all odd-numbered switches (602b) of the three or more switches (602a, 602b) on the first arm, counting from the first switch to the last switch along the first arm.

9. The method (700) according to claim 7 or 8, It is characterized in that The third group of switches includes all even-numbered switches (602c) of the three or more switches (602c, 602d) on the second arm, counted from the first switch to the last switch along the second arm; The fourth group of switches includes all odd-numbered switches (602d) of the three or more switches (602c, 602d) on the second arm, counted from the first switch to the last switch along the second arm.

10. The method (700) according to any one of claims 1 to 9, It is characterized in that Also includes: regrouping the three or more switches (602a, 602b) on the first arm from the first group of switches and the second group of switches into a fifth group of switches and a sixth group of switches; To achieve the fourth Q2L pulse, Simultaneously turning on each switch (140a) in the fifth set of switches; Then, each switch in the sixth group of switches is turned on simultaneously (140b); simultaneously opening (140a) each switch in the fifth set of switches after a pulse duration of the fourth Q2L pulse, wherein the pulse duration of the fourth Q2L pulse begins when each switch in the fifth set of switches is turned on; Each switch in the sixth set of switches is then opened simultaneously (140b).

11. The method (700) according to claim 10, It is characterized in that The regrouping is performed if a charging rate of at least one of the first flying capacitor (601a) and the second flying capacitor (601b) is different from a discharging rate of the at least one flying capacitor.

12. The method (700) according to claim 10 or 11, It is characterized in that The regrouping is performed when a voltage of at least one of the first flying capacitor (601a) and the second flying capacitor (601b) reaches a corresponding threshold voltage.

13. A controller for controlling a flying capacitor converter (FCC) (100, 600, 800) according to quasi-2-level (Q2L) modulation, It is characterized in that The FCC (100, 600, 800) comprises at least two flying capacitors (601a, 601b), a first arm and a second arm, wherein each arm comprises at least three series switches (602a, 602b, 602c, 602d), one of the two terminals of each flying capacitor (601a, 601b) is connected to the first arm, the other terminal is connected to the second arm, and the two terminals of each flying capacitor (601a, 601b) are connected between corresponding pairs of switches (602a, 602b) on the two arms; The controller is used to: in order to achieve the first Q2L pulse, Simultaneously controlling each switch (602a) of a first group of switches of the three or more switches (602a, 602b) on the first arm to be turned on; Then, each switch (602b) in the second group of the three or more switches (602a, 602b) on the first arm is controlled to be turned on simultaneously; After a pulse duration of the first Q2L pulse, simultaneously controlling each switch in the first set of switches (602a) to be turned off, wherein the pulse duration of the first Q2L pulse starts when each switch in the first set of switches (602a) is controlled to be turned on; Then, each switch (602b) in the second group of switches is simultaneously controlled to be opened.

14. A flying capacitor converter (FCC) device, It is characterized in that It comprises an FCC (100, 600, 800) according to claim 13 and a controller.

15. A computer program comprising instructions, It is characterized in that When the program is executed by a processing device such as a controller according to claim 13, the instructions cause the processing device to control the FCC (100, 600, 800) to operate according to the method (700) of any one of claims 1 to 12.

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